TerelNewton.com - TOPICALS FOR PAIN 26

TerelNewton.com

Category 1 — Very large molecules>1,000 g/mol

1.Botulinum toxin A~150,000 g/molNeurotoxin; focal neuropathic pain; injected locally

Category 2 — Large molecules300–500 g/mol

2.Indomethacin358 g/molNSAID; inflammatory pain

3.Piroxicam331 g/molNSAID; acute musculoskeletal pain

4.Cannabidiol (CBD)314 g/molCannabinoid; peripheral neuropathy; limited evidence

5.Δ9-THC314 g/molCannabinoid; neuropathic pain; bioavailability concerns topically

6.Capsaicin305 g/molTRPV1 agonist; neuropathic pain (NNT 10.6 for 8% patch)

7.Diclofenac296 g/molNSAID; OA, sprains (NNT 1.8–5.0); best-studied topical NSAID

8.Bupivacaine288 g/molLocal anesthetic; compounded formulations

9.Doxepin279 g/molTricyclic antidepressant; neuropathic pain, pruritus

10.Amitriptyline277 g/molTricyclic antidepressant; compounded neuropathic pain

11.Tetracaine264 g/molLocal anesthetic; topical anesthesia

12.Arnica (helenalin)262 g/molHerbal; bruises, muscle soreness

13.Ketoprofen254 g/molNSAID; sprains, strains, OA; good evidence

14.Phenytoin252 g/molAnticonvulsant; compounded neuropathic pain

Category 3 — Medium molecules200–299 g/mol

15.Flurbiprofen244 g/molNSAID; musculoskeletal pain

16.Ketamine238 g/molNMDA antagonist; compounded neuropathic pain

17.Lidocaine234 g/molLocal anesthetic; neuropathic pain (NNT 4.4); first-line topical

18.Naproxen230 g/molNSAID; musculoskeletal pain

19.Clonidine230 g/molAlpha-2 agonist; compounded neuropathic pain

20.Glyceryl trinitrate (nitroglycerin)227 g/molVasodilator; rotator cuff tendinopathy; diabetic neuropathy

21.Prilocaine220 g/molLocal anesthetic; EMLA cream (with lidocaine)

22.Baclofen214 g/molGABA-B agonist; compounded neuropathic pain

23.Ibuprofen206 g/molNSAID; musculoskeletal pain

Category 4 — Small molecules150–199 g/mol

24.Gabapentin171 g/molAnticonvulsant; compounded neuropathic pain

25.Benzocaine165 g/molLocal anesthetic; superficial pain/itch

26.Eugenol (clove oil)164 g/molNatural/essential oil; dental/muscle pain

27.Menthol156 g/molCounterirritant; muscle aches, cooling sensation

28.Camphor152 g/molCounterirritant; muscle pain, rubefacient

29.Methyl salicylate152 g/molSalicylate; muscle/joint pain

Category 5 — Very small molecules<150 g/mol

30.Salicylic acid138 g/molSalicylate; rubefacient, keratolytic

🔑 Key clinical pearls

Optimal skin penetration: molecules <500 Da + moderate lipophilicity; all except botulinum toxin meet this criterion

Best evidence (SORT A): diclofenac, ketoprofen, lidocaine 5%, capsaicin 8%

Compounded formulations (ketamine, baclofen, gabapentin, amitriptyline) cost ~$55–150/month; not insurance-covered

OTHER COMMON TOPICALS..

LIST #1

Category 1 — Macromolecules & steroids>400 g/mol

1.Tacrolimus (Protopic)804 g/molCalcineurin inhibitor; eczema/psoriasis

2.Halobetasol propionate485 g/molSuper-potent corticosteroid; psoriasis

3.Clobetasol propionate467 g/molSuper-potent corticosteroid; Class I

4.Betamethasone dipropionate504 g/molPotent corticosteroid; Class II

5.Fluocinonide495 g/molPotent corticosteroid; dermatitis

6.Triamcinolone acetonide434 g/molMid-potency corticosteroid; Class III–IV

7.Mometasone furoate521 g/molMid-potency corticosteroid; Class IV

8.Hydrocortisone butyrate432 g/molMid-potency corticosteroid; Class V

9.Tretinoin (retinoic acid)300 g/molRetinoid; acne, photoaging; borderline large

10.Calcipotriene (Dovonex)412 g/molVitamin D analogue; psoriasis

Category 2 — Antifungals & antivirals250–450 g/mol

11.Econazole nitrate444 g/molAzole antifungal; tinea, candida

12.Ketoconazole531 g/molAzole antifungal; seborrheic dermatitis

13.Clotrimazole344 g/molAzole antifungal; tinea, candida

14.Miconazole416 g/molAzole antifungal; OTC tinea/candida

15.Terbinafine (Lamisil)291 g/molAllylamine antifungal; onychomycosis

16.Acyclovir (topical)225 g/molAntiviral; HSV labialis; limited penetration

17.Penciclovir (Denavir)253 g/molAntiviral; cold sores; better topical than acyclovir

18.Imiquimod (Aldara)240 g/molImmune modifier; genital warts, AK

Category 3 — Antibiotics & antiseptics150–500 g/mol

19.Mupirocin (Bactroban)501 g/molAntibiotic; impetigo, MRSA decolonization

20.Fusidic acid516 g/molAntibiotic; staphylococcal skin infections

21.Clindamycin (topical)425 g/molAntibiotic; acne vulgaris

22.Metronidazole (topical)171 g/molAntibiotic; rosacea; small molecule

23.Erythromycin (topical)734 g/molMacrolide antibiotic; acne; very large

24.Neomycin sulfate615 g/molAminoglycoside; wound infections; high sensitization

25.Bacitracin~1,423 g/molPolypeptide antibiotic; OTC wound care

26.Povidone-iodine~2,364 g/molAntiseptic polymer-iodine complex; wound care

27.Chlorhexidine505 g/molAntiseptic; wound/skin disinfection

Category 4 — Dermatologics & vasodilators100–350 g/mol

28.Minoxidil209 g/molVasodilator; alopecia; Rogaine

29.Finasteride (topical)373 g/mol5α-reductase inhibitor; compounded hair loss

30.Hydroquinone110 g/molDepigmenting agent; melasma; very small

31.Azelaic acid188 g/molDicarboxylic acid; rosacea, acne, melasma

32.Benzoyl peroxide242 g/molOxidizing agent; acne; bactericidal

33.Pimecrolimus (Elidel)810 g/molCalcineurin inhibitor; atopic dermatitis; large

34.Coal tar~variableComplex mixture; psoriasis, seborrheic dermatitis

Category 5 — Ophthalmics & small actives<250 g/mol

35.Timolol (ophthalmic)316 g/molBeta-blocker; glaucoma eye drops

36.Latanoprost432 g/molProstaglandin analogue; glaucoma

37.Brimonidine (Mirvaso)292 g/molAlpha-2 agonist; rosacea erythema; topical gel

38.Fluorouracil (5-FU)130 g/molAntimetabolite; actinic keratosis; Efudex

39.Urea (40%)60 g/molKeratolytic; hyperkeratosis; smallest common topical

40.Lactic acid90 g/molAHA keratolytic; ichthyosis, xerosis

LIST #2

🔬 CATEGORY 1: Large Molecules — Near/Above 500 Da Limit (Poor Penetration)

Tacrolimus — 804 g/mol — Calcineurin inhibitor; atopic dermatitis (requires thin skin for absorption)
[1]
Cyclosporine (topical) — 1,203 g/mol — Immunosuppressant; poor topical penetration confirms 500 Da rule
[1]
Mupirocin — 501 g/mol — Antibiotic; impetigo, MRSA decolonization
[3]
Pimecrolimus — 810 g/mol — Calcineurin inhibitor; atopic dermatitis
[1]
Nystatin — 926 g/mol — Polyene antifungal; cutaneous candidiasis (works on surface only)
[4]

🧪 CATEGORY 2: Corticosteroids (360–525 g/mol)

Clobetasol propionate — 467 g/mol — Class I (super-potent); psoriasis, severe eczema
[5]
Halobetasol propionate — 485 g/mol — Class I (super-potent); psoriasis
[5]
Betamethasone dipropionate — 504 g/mol — Class I–II; psoriasis, dermatitis
[5]
Fluocinonide — 495 g/mol — Class II (high potency); eczema, dermatitis
[5]
Triamcinolone acetonide — 434 g/mol — Class II–IV; versatile mid-potency steroid
[5]
Mometasone furoate — 521 g/mol — Class II–IV; dermatitis, psoriasis
[5]
Fluticasone propionate — 501 g/mol — Class III–V; eczema, dermatitis
[5]
Hydrocortisone acetate — 405 g/mol — Class VII (lowest potency); mild dermatitis
[5-7]
Hydrocortisone — 362 g/mol — Class VII; OTC anti-itch, mild eczema
[6-7]
Desonide — 416 g/mol — Class VI (low potency); pediatric eczema
[5]

💊 CATEGORY 3: Antibiotics & Antiseptics (130–480 g/mol)

Fusidic acid — 517 g/mol — Antibiotic; staphylococcal skin infections
[8]
Erythromycin (topical) — 734 g/mol — Antibiotic; acne (surface action)
[3]
Clindamycin — 425 g/mol — Antibiotic; acne vulgaris
[9]
Metronidazole — 171 g/mol — Antibiotic/anti-inflammatory; rosacea
Bacitracin — 1,423 g/mol — Antibiotic; wound care (surface action only)
[3]
Neomycin — 615 g/mol — Antibiotic; wound care (contact dermatitis risk)
[3]
Benzoyl peroxide — 242 g/mol — Antimicrobial/keratolytic; acne
[9]
Silver sulfadiazine — 357 g/mol — Antimicrobial; burn wounds

🍄 CATEGORY 4: Antifungals (250–450 g/mol)

Ketoconazole — 531 g/mol — Azole antifungal; seborrheic dermatitis, tinea
[4][10]
Clotrimazole — 345 g/mol — Azole antifungal; tinea, candidiasis
[10-11]
Miconazole — 416 g/mol — Azole antifungal; tinea, candidiasis
[8][10]
Terbinafine — 291 g/mol — Allylamine antifungal (fungicidal); tinea pedis, corporis
[10][12]
Ciclopirox — 207 g/mol — Hydroxypyridone; onychomycosis, seborrheic dermatitis
[12]
Efinaconazole — 348 g/mol — Azole; onychomycosis (newer agent)
[12]
Tavaborole — 152 g/mol — Oxaborole; onychomycosis (smallest antifungal)
[12]

🧴 CATEGORY 5: Retinoids & Other Dermatologics (150–350 g/mol)

Tretinoin (all-trans retinoic acid) — 300 g/mol — Retinoid; acne, photoaging
[13]
Adapalene — 412 g/mol — Synthetic retinoid; acne (anti-inflammatory)
[13]
Tazarotene — 351 g/mol — Retinoid prodrug; acne, psoriasis
[13]
Hydroquinone — 110 g/mol — Depigmenting agent; melasma, PIH
[9]
Azelaic acid — 188 g/mol — Anti-inflammatory/tyrosinase inhibitor; rosacea, PIH
[9]
Calcipotriol (calcipotriene) — 413 g/mol — Vitamin D analog; psoriasis
Roflumilast — 403 g/mol — PDE4 inhibitor; psoriasis, seborrheic dermatitis
[14]
5-Fluorouracil — 130 g/mol — Antimetabolite; actinic keratoses, superficial BCC
Imiquimod — 240 g/mol — Immune response modifier; actinic keratoses, BCC, warts
Minoxidil — 209 g/mol — Vasodilator; androgenetic alopecia

Key Takeaway — The 500 Dalton Rule:

Molecules <500 Da penetrate skin effectively; virtually all successful topical drugs fall below this threshold.

[1]

Notable exceptions (tacrolimus 804 Da, pimecrolimus 810 Da) work because they are applied to disrupted skin barriers in eczema, not intact skin.

[1]

This rule is critical when evaluating whether a compound can realistically achieve therapeutic concentrations topically.

[2]

Page updated

Google Sites

Report abuse